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Seek to understand the molecular mechanism by which human telomerase (hTERT) promoter mutations contribute to the biology of tumor cells.

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Multiple modes of regulation of the human Ino80 SNF2 ATPase by subunits of the INO80 chromatin-remodeling complex.Proceedings of the National Academy of Sciences of the United States of AmericaChen, L., Conaway, R. C., Conaway, J. W.2013; 110 (51): 20497?502

Abstract

SNF2 family ATPases are ATP-dependent motors that often function in multisubunit complexes to regulate chromatin structure. Although the central role of SNF2 ATPases in chromatin biology is well established, mechanisms by which their catalytic activities are regulated by additional subunits of chromatin-remodeling complexes are less well understood. Here we present evidence that the human Inositol auxotrophy 80 (Ino80) SNF2 ATPase is subject to regulation at multiple levels in the INO80 chromatin-remodeling complex. The zinc finger histidine triad domain-containing protein Ies2 (Ino Eighty Subunit 2) functions as a potent activator of the intrinsic catalytic activity of the Ino80 ATPase, whereas the YL-1 family Ies6 (Ino Eighty Subunit 6) and actin-related Arp5 proteins function together to promote binding of the Ino80 ATPase to nucleosomes. These findings support the idea that both substrate recognition and the intrinsic catalytic activities of SNF2 ATPases have evolved as important sites for their regulation.

Abstract

We previously identified and purified a human ATP-dependent chromatin remodeling complex with similarity to the Saccharomyces cerevisiae INO80 complex (Jin, J., Cai, Y., Yao, T., Gottschalk, A. J., Florens, L., Swanson, S. K., Gutierrez, J. L., Coleman, M. K., Workman, J. L., Mushegian, A., Washburn, M. P., Conaway, R. C., and Conaway, J. W. (2005) J. Biol. Chem. 280, 41207-41212) and demonstrated that it is composed of (i) a Snf2 family ATPase (hIno80) related in sequence to the S. cerevisiae Ino80 ATPase; (ii) seven additional evolutionarily conserved subunits orthologous to yeast INO80 complex subunits; and (iii) six apparently metazoan-specific subunits. In this report, we present evidence that the human INO80 complex is composed of three modules that assemble with three distinct domains of the hIno80 ATPase. These modules include (i) one that is composed of the N terminus of the hIno80 protein and all of the metazoan-specific subunits and is not required for ATP-dependent nucleosome remodeling; (ii) a second that is composed of the hIno80 Snf2-like ATPase/helicase and helicase-SANT-associated/post-HSA (HSA/PTH) domain, the actin-related proteins Arp4 and Arp8, and the GLI-Kruppel family transcription factor YY1; and (iii) a third that is composed of the hIno80 Snf2 ATPase domain, the Ies2 and Ies6 proteins, the AAA(+) ATPases Tip49a and Tip49b, and the actin-related protein Arp5. Through purification and characterization of hINO80 complex subassemblies, we demonstrate that ATP-dependent nucleosome remodeling by the hINO80 complex is catalyzed by a core complex comprising the hIno80 protein HSA/PTH and Snf2 ATPase domains acting in concert with YY1 and the complete set of its evolutionarily conserved subunits. Taken together, our findings shed new light on the structure and function of the INO80 chromatin-remodeling complex.

Abstract

CSB/ERCC6 (Cockayne syndrome B protein/excision repair cross-complementation group 6), a member of a subfamily of SWI2/SNF2 (SWItch/sucrose nonfermentable)-related chromatin remodelers, plays crucial roles in gene expression and the maintenance of genome integrity. Here, we report the mechanism of the autoregulation of Rhp26, which is the homolog of CSB/ERCC6 in Schizosaccharomyces pombe. We identified a novel conserved protein motif, termed the "leucine latch," at the N terminus of Rhp26. The leucine latch motif mediates the autoinhibition of the ATPase and chromatin-remodeling activities of Rhp26 via its interaction with the core ATPase domain. Moreover, we found that the C terminus of the protein counteracts this autoinhibition and that both the N- and C-terminal regions of Rhp26 are needed for its proper function in DNA repair in vivo. The presence of the leucine latch motif in organisms ranging from yeast to humans suggests a conserved mechanism for the autoregulation of CSB/ERCC6 despite the otherwise highly divergent nature of the N- and C-terminal regions.

Abstract

Members of the SNF2 family of ATPases often function as components of multi-subunit chromatin remodeling complexes that regulate nucleosome dynamics and DNA accessibility by catalyzing ATP-dependent nucleosome remodeling. Biochemically dissecting the contributions of individual subunits of such complexes to the multi-step ATP-dependent chromatin remodeling reaction requires the use of assays that monitor the production of reaction products and measure the formation of reaction intermediates. This JOVE protocol describes assays that allow one to measure the biochemical activities of chromatin remodeling complexes or subcomplexes containing various combinations of subunits. Chromatin remodeling is measured using an ATP-dependent nucleosome sliding assay, which monitors the movement of a nucleosome on a DNA molecule using an electrophoretic mobility shift assay (EMSA)-based method. Nucleosome binding activity is measured by monitoring the formation of remodeling complex-bound mononucleosomes using a similar EMSA-based method, and DNA- or nucleosome-dependent ATPase activity is assayed using thin layer chromatography (TLC) to measure the rate of conversion of ATP to ADP and phosphate in the presence of either DNA or nucleosomes. Using these assays, one can examine the functions of subunits of a chromatin remodeling complex by comparing the activities of the complete complex to those lacking one or more subunits. The human INO80 chromatin remodeling complex is used as an example; however, the methods described here can be adapted to the study of other chromatin remodeling complexes.

Abstract

INO80 chromatin remodeling complexes regulate nucleosome dynamics and DNA accessibility by catalyzing ATP-dependent nucleosome remodeling. Human INO80 complexes consist of 14 protein subunits including Ino80, a SNF2-like ATPase, which serves both as the catalytic subunit and the scaffold for assembly of the complexes. Functions of the other subunits and the mechanisms by which they contribute to the INO80 complex's chromatin remodeling activity remain poorly understood, in part due to the challenge of generating INO80 subassemblies in human cells or heterologous expression systems. This JOVE protocol describes a procedure that allows purification of human INO80 chromatin remodeling subcomplexes that are lacking a subunit or a subset of subunits. N-terminally FLAG epitope tagged Ino80 cDNA are stably introduced into human embryonic kidney (HEK) 293 cell lines using Flp-mediated recombination. In the event that a subset of subunits of the INO80 complex is to be deleted, one expresses instead mutant Ino80 proteins that lack the platform needed for assembly of those subunits. In the event an individual subunit is to be depleted, one transfects siRNAs targeting this subunit into an HEK 293 cell line stably expressing FLAG tagged Ino80 ATPase. Nuclear extracts are prepared, and FLAG immunoprecipitation is performed to enrich protein fractions containing Ino80 derivatives. The compositions of purified INO80 subcomplexes can then be analyzed using methods such as immunoblotting, silver staining, and mass spectrometry. The INO80 and INO80 subcomplexes generated according to this protocol can be further analyzed using various biochemical assays, which are described in the accompanying JOVE protocol. The methods described here can be adapted for studies of the structural and functional properties of any mammalian multi-subunit chromatin remodeling and modifying complexes.

Abstract

Transcription factor ATF6? functions as a master regulator of endoplasmic reticulum (ER) stress response genes. In response to ER stress, ATF6? translocates from its site of latency in the ER membrane to the nucleus, where it activates RNA polymerase II transcription of ER stress response genes upon binding sequence-specifically to ER stress response enhancer elements (ERSEs) in their promoter-regulatory regions. In a recent study, we demonstrated that ATF6? activates transcription of ER stress response genes by a mechanism involving recruitment to ERSEs of the multisubunit Mediator and several histone acetyltransferase (HAT) complexes, including Spt-Ada-Gcn5 (SAGA) and Ada-Two-A-containing (ATAC) (Sela, D., Chen, L., Martin-Brown, S., Washburn, M.P., Florens, L., Conaway, J.W., and Conaway, R.C. (2012) J. Biol. Chem. 287, 23035-23045). In this study, we extend our investigation of the mechanism by which ATF6? supports recruitment of Mediator to ER stress response genes. We present findings arguing that Mediator subunit MED25 plays a critical role in this process and identify a MED25 domain that serves as a docking site on Mediator for the ATF6? transcription activation domain.

Abstract

The basic leucine zipper transcription factor ATF6? functions as a master regulator of endoplasmic reticulum (ER) stress response genes. Previous studies have established that, in response to ER stress, ATF6? translocates to the nucleus and activates transcription of ER stress response genes upon binding sequence specifically to ER stress response enhancer elements in their promoters. In this study, we investigate the biochemical mechanism by which ATF6? activates transcription. By exploiting a combination of biochemical and multidimensional protein identification technology-based mass spectrometry approaches, we have obtained evidence that ATF6? functions at least in part by recruiting to the ER stress response enhancer elements of ER stress response genes a collection of RNA polymerase II coregulatory complexes, including the Mediator and multiple histone acetyltransferase complexes, among which are the Spt-Ada-Gcn5 acetyltransferase (SAGA) and Ada-Two-A-containing (ATAC) complexes. Our findings shed new light on the mechanism of action of ATF6?, and they outline a straightforward strategy for applying multidimensional protein identification technology mass spectrometry to determine which RNA polymerase II transcription factors and coregulators are recruited to promoters and other regulatory elements to control transcription.